Title

Antiplasticization of polyimides

Date of Completion

January 1993

Keywords

Chemistry, Polymer|Plastics Technology

Degree

Ph.D.

Abstract

Amorphous and semi-crystalline polymers may be antiplasticized by low molecular weight organic materials. An antiplasticized polymer is characterized by a higher modulus, higher ultimate strength, lower ultimate elongation, and lower glass transition temperature ($T\sb{g})$ than the neat polymer. These properties result from reduction of polymer molecular mobility. Reduced mobility has been linked to less free volume, which reduces the room for movement, and polymer-additive interactions, which lock polymer segments in place. This is the first detailed study of antiplasticization in polyimides.^ Initial studies to determine the physical and chemical state of antiplasticized polyimides were carried out with the additive, N-(4-(2-hydroxy-3-phenoxypropoxy) phenyl) acetamide (EPPHAA). Three commercial polyimides, PI-2540 (DuPont), Durimid 100 (Rogers), and Matrimid 5218 (Ciba-Geigy), were antiplasticized to various extents and over different temperature ranges. The tensile moduli and tensile breaking strengths were increased by 25% to 40% and 7% to 27%, respectively, at room temperature. The elongations at break were reduced by at least 50%. Quantitative size exclusion chromatographic (SEC) analysis and dynamic mechanical analysis (DMA) of extracted polyimide/EPPHAA films showed that EPPHAA was completely separable from these polyimides following thermal treatment to remove solvent and affect imidization of the polyamic acids. SEC and infrared spectroscopic (IR) analyses indicated no effect on molecular weight or molecular weight distribution and no covalent bonding between polyamic acid and EPPHAA.^ A combination of free volume measurements, solubility parameter comparisons, and DMA results led to conclusions of the molecular characteristics of both polyimides and additives which determined antiplasticization effectiveness. Fluorene, 9-fluorenone, 2-acetamidofluorene, 9-hydroxyfluorene, and 2,4,7-trichlorofluorene were used as additives in addition to EPPHAA for this purpose. All of the additives had nearly the same effect on free volume in Matrimid 5218, while there was more variation in free volume in PI-2540/additive mixtures. Therefore, in PI-2540/additive mixtures, both polymer-additive interactions and molecular mobility were seen to influence free volume. These could not be distinguished in Matrimid 5218/additive mixtures. The modulus was found not to be determined by free volume, but by the molecular mobility of the polymer molecules, which was influenced by the mobility of the additive molecules. The influence of additive mobility was seen in differences in the mechanical relaxation spectra of the various polymer/additive films. ^